Water the lawn thoroughly, apply fertilizer, and overseed if necessary to promote healthy growth.

Johnsongrass and crabgrass are invasive weeds that can overtake your lawn. Crabgrass is a low-growing grass most often seen in lawns, flower beds, and vegetable gardens. While you may find Johnsongrass growing in your lawn, it will also grow in pastures, crop fields, and the edge of the road. Johnsongrass is much coarser than crabgrass. If left alone, Johnsongrass can grow up to 8 feet tall. 

Whether a one-time spray treatment to control mosquitoes is enough depends on multiple factors. Often, you’ll notice a big difference after one application. However, mosquitoes are likely to return if you don't reduce attractive standing water habitats. This usually takes four to eight weeks if it’s still prime mosquito season.

Landscape fabric and a few inches of gravel should be enough to put under a deck to prevent weeds from flourishing. If you don’t want to invest the time and money on a project like this, you can regularly spray the area underneath your deck to kill weeds.